The invention is based on a power grinder, having a motor and a gear that drive an oscillating drive means about a deflection angle; the drive means drives a grinding belt, secured to it, to reciprocate.
For machining round objects in the built-in state, it is necessary for the grinding belt to adapt to the radius of that object. Moreover, there must be a possibility of releasing or closing the grinding belt. This is attained, by the devices available on the market, by means of an endless grinding belt. If built-in objects are to be ground, the grinding belt must be severed and then glued together again afterward. This is very complicated and expensive.
From German Patent Disclosure DE 34 47 828 A1, a motor-drivable grinding apparatus is also known, which is used for grinding, smoothing and polishing of preferably round bars and tubes. It uses an open grinding belt, wrapped in a loop around the workpiece, that is held by its two ends in two clamping or tensioning devices of the grinding apparatus. Via a movement device, a gear that can be driven by motor in a rotary motion in the same direction sets the two clamping and tensioning devices and thus also the grinding belt into an alternating, synchronized opposed motion, which pulls the grinding belt over the workpiece. Thus the grinding action is attained. Although such an oscillating motion enables high operating safety and good manipulation of the grinding apparatus, nevertheless the effort and expense for changing the grinding means is very high, since the grinding belt has to be removed with its ends from the clamping or tensioning device, and the new grinding belt has to be inserted back into this device.
A power grinder according to the invention has the advantage over the prior art that a simple change of the grinding belt is possible. By means of the closure on the grinding belt, it is unnecessary to perform complicated cutting apart and gluing of the grinding belt, or releasing and securing the ends from and to a clamping or tensioning device. The release and securing of the grinding belt is done for instance in the case of a hook-and-loop closure by simple pressing actions, without requiring additional steps. Moreover, the hook-and-loop closure offers adequately high security against an unintended release.
It is advantageous if the closure is in engagement with the drive means. To that end, in the case of a hook-and-loop closure, for instance, the grinding belt is first wrapped around the object to be machined and is then pressed with its two ends against the drive means; the counterparts of the hook-and-loop closure of the grinding belt are disposed on the drive means. Another option is to guide the grinding belt, once it has been wrapped around the object to be machined, all the way around the entire drive means and to join the two ends of the grinding belt directly to one another, between the drive means and the object to be machined, by means of a hook-and-loop closure.
It is especially advantageous if the drive means is a swing head, which in particular takes the form of a wheel. As a result, it is possible in a simple way to wrap the grinding belt around the swing head and secure it to the swing head, or to connect its two ends together, between the swing head and the workpiece to be machined, as described above.
It is also advantageous if the face end of the gear, on its side remote from the motor, has a beveled drive shaft on which a peg that is in engagement with the drive means is disposed eccentrically. As a result, the driving motion, as a rule rotation, that is imparted by the gear is converted into an oscillating motion. This is done in a way that is very simple to achieve and is not very complicated structurally. It is especially preferred if the peg is seated in a sliding block guide on the drive means.
It is also preferred if the closure is embodied on the first end and on the second end of the grinding belt. Compared to being disposed inside the grinding belt, the entire length of the grinding belt can thus be utilized. This contributes to making it possible for round objects with quite different diameters to be machined with the same grinding belt.
Another feature according to the invention provides that the grinding belt is disposed with its first end on the drive means and its second end is connected to a handle. Once again, this makes simple changing of the grinding belt possible. It is also thereby especially simply possible to wrap the grinding belt around the object to machined, since the grinding belt does not have to be released from its fastening points at all.
It is advantageous if an elastic element, is disposed between the second end of the grinding belt and the handle. As a result, the oscillating motion of the grinding belt is not transmitted in full to the handle and hence to the hand of the user.
It is also advantageous if the first end of the grinding belt is mounted rotatably on the drive means. As a result, in places that are hard to reach but need to be machined, this makes it possible for the user not to have to assume unnatural hand and arm positions.
It is also advantageous if the drive means is a machine insert. As a result, the grinder is universally usable, since still other inserts besides the grinding belt can be coupled to the machine insert.
Further advantageous features of the invention are the subject of the dependent claims.